30mil Magnetic Strip with Rounded Corners will hold up to repeated opening and closing of doors. Never worry about wasting precious seconds searching for keys and fumbling to lock a door. LOCKDOWN Magnetic Strips are a fast, easy, budget-friendly solution to help secure classrooms during a lockdown or emergency. We have designed effective lockdown magnetic strips printed with easy-to-use instructions which will allow teachers & substitute teachers to lock a classroom door lightning FAST without any keys! Easy 1-2-3 Instructions printed directly on the Lockdown magnetic Strip: Step 1) Lock the Door; Step 2) Cover the latch plate with LOCKDOWN Magnetic Strip; Step 3) Keep Door Locked, Open & Close Door with Magnetic Strip in place. During a Lockdown or Emergency, Simply Remove LOCKDOWN Magnetic Strip & Close Door. Consult with your school security team to ensure use of magnetic lockdown strips is permitted at your facility. One color per pack. Colors may vary. WARNING! – DO NOT USE LOCKDOWN MAGNETIC STRIPS ON FIRE DOORS OR EMERGENCY EXITS! 1.We recommend consulting with your school district and/or school security guidelines prior to purchase to confirm that use of this product is permitted in your classroom. 2.This product will not work with some doors, particularly those with little or no metal exposure on the latch plate. We suggest that you purchase our 10 Pack of Lockdown Magnetic Strips for testing prior to making a bulk purchase.